Today, global climate change and energy national security as well as improvement of air quality, are absolute global priorities. Most cellulosic biofuels technologies are designed to produce gasoline blendstocks such as ethanol. Diesel cellulosic fuels would reduce greenhouse emissions. A cellulosic fuel that is a viable turbine fuel with application to the renewable jet fuel market would also be of great benefit for climate change mitigation and energy national security.
Although cellulose is the most abundant plant material resource, its exploitation has been curtailed by its composite nature and rigid structure. As a result, most technical approaches to convert lignocellulosic material to fuel products have focused on an effective pretreatment to liberate the cellulose from the lignin composite and break down its rigid structure. Besides effective cellulose liberation, a favorable pretreatment can minimize the formation of degradation products because of their wastefulness and inhibitory effects on subsequent processes. One way to improve the efficiency of biomass conversion schemes (biorefineries) is to integrate the energy-intensive lignocellulose depolymerization and dehydration (LDD) process with power production and/or other biomass processing. Some biorefineries rely on conversion of lignocellulose to glucose and subsequent fermentation, but this processing can require expensive enzymes and long contact times or can produce compounds that inhibit the fermentation or that are low-value by-products. In addition, fermentation releases carbon dioxide and produces cell mass, which in some examples can only be efficiently reused as a livestock supplement.
An alternative processing for lignocellulosic materials is acid-catalyzed depolymerization and conversion to the C5 product, levulinic acid, or esters thereof. In general, two methods are used to produce levulinic acid or levulinate ester from lignocellulose. One method uses water with a strong acid catalyst, such as sulfuric acid, to effect the depolymerization and dehydration of lignocellulose to produce the C5 and C1 acids (levulinic and formic acids) (see, for example, U.S. Pat. No. 5,608,105). However, separation of products from the aqueous product solution is difficult. One patent describes a separation scheme that uses an olefin feed to convert the aqueous acid to esters that can be separated from the water and each other (see, for example, U.S. Pat. No. 7,153,996). Of course, a nearby olefin source is required for this process.
Another method uses an alcohol solvent for the acid-catalyzed depolymerization of cellulose, which results in direct formation of the levulinate ester (see, for example, DE 3621517).
Another method of liquid phase catalytic conversion of C6 sugars and the cellulose component of lignocellulosic materials into intermediates for fuel production is described in by Mascal (U.S. Pat. No. 7,829,732 B2), in which chloromethylfurfural (CMF) is formed in high yield.
Another method of liquid phase catalytic conversion of C6 sugars into intermediates, predominately hydroxymethylfurfural (HMF) and further processing for fuel production, is described in by Dumesic (U.S. Pat. No. 7,880,049), in which hydroxymethylfurfural (HMF) is formed in high yield and either self condensed or cross condensed with another aldehydes or ketone before deoxygenating to alkane based fuels.
Published U.S. Patent Application US 2010/0312028 describes a multiproduct biorefinery based on producing levulinic acid or esters thereof from C6 sugar sources, condensing the levulinate with another aldehyde and deoxygenating the condensation products to alkane fuels and other products.